Traveling concrete extrusion machines are typically used for the making hollow core concrete slabs. These machines have a hopper which receives premixed concrete. The concrete falls into a feed chamber which is mounted on a frame. The machines also have a molding chamber where the concrete is molded into the profile of the slab. One or more spiral conveyors push the concrete from the feed chamber towards the molding chamber and, at the same time, propel the machine in the opposite direction. Each of the spiral conveyors is rotatable about a non-rotating mandrel shaft. A series of mandrels with internal vibrators are connected to the shaft. Similar machines are disclosed, for example, in my earlier U.S. Pat. No. 4,330,242.
The compression on the concrete in the molding chamber is increased where the spiral conveyors have tapered sections such that the flights of each conveyor are larger in diameter towards the molding chamber compared with flights closer to the feed chamber. This arrangement is shown, for example, in my British Patent No. 1,342,601. However, wear is accentuated at the end of the spiral conveyor adjacent to the mandrels. This leads to a rounding off of the conveyor flights in this location and a corresponding reduction in the compression effect otherwise achieved by such a tapered spiral conveyor.
Replacing the spiral conveyors is an expensive proposition since they are made of a special high chromium iron alloy. Moreover this involves dismantling the extrusion machine with attendant high labor costs and loss of production. Accordingly, attempts have been made to provide replaceable sections on the spiral conveyors where wear is most extreme. Such an arrangement is shown, for example, in Canadian patent 1,205,985 to Kiss. This patent shows a conveyor with a replaceable section made in two halves. These halves are connected to the main portion of the main auger by bolts.
However, these bolts are often shaken loose by vibrators in the mandrel. The loose bolts allow halves of the conveyor to disconnect and can cause damage to the machine. Alternatively, the vibrations of the mandrels can cause the bolts to become welded to the main auger. Thus the bolts break off when attempts are made to loosen them to replace the sections of the spiral conveyors.
It is an object of the invention to provide an improved spiral conveyor for a concrete extrusion machine which has a tapered profile, but significantly reduces the wear which is normally concentrated at the end of the conveyor adjacent the mandrels.
It is also an object of the invention to provide an improved spiral conveyor for a concrete extrusion machine which has a replaceable section in a high wear location, but is not adversely affected by vibrations in the mandrel or other parts of the machine since it is not connected to the main auger by bolts or the like.
It is a still further object of the invention to provide an improved spiral conveyor with a replaceable section which can be easily removed and replaced with a new section without undue labor costs or loss of production of the machine.
According to one aspect of the invention, there is provided a spiral conveyor for a concrete extrusion machine which has a first spiral conveyor section having a first length and a first external diameter. A second spiral conveyor section is straight and has a second external diameter, which is greater than the first external diameter, and a second length. The first section is spaced apart from the second section A third spiral conveyor section is between the first section and the second section. The third section is tapered, has a third length, a first end being adjacent to the first section and a second end being adjacent to the second section. The first section maybe straight. The first end has the first external diameter and the second end has the second external diameter. There is means for mounting the spiral conveyor in the extrusion machine.
According to another aspect of the invention, there is provided a spiral conveyor for a concrete extrusion machine. The conveyor has a first spiral conveyor section and a shaft extending axially from the first section. A second spiral conveyor section is mounted on the shaft. The second section has two symmetrical halves. Each half has a semi-cylindrical recess therein. Connectors interconnect the two halves and a locking device is between the shaft and the second section The two halves are not connected to the mandrel shaft.
According to a further aspect of the invention, there is provided a traveling extrusion machine for forming hollow core concrete sections. The machine has a frame and a feed chamber mounted on the frame for receiving premixed concrete. A molding chamber is adjacent to the feed chamber. There is a mandrel in the molding chamber and a vibrator mounted in the mandrel. A rotatable spiral conveyor extends from the feed chamber toward the molding chamber. The conveyor has a hallow shaft adjacent the mandrel and a section of the spiral conveyor is releasably mounted on the shaft. The section of the conveyor includes two halves on opposite sides of the shaft. A non-rotation locking device is between the halves and the shaft. Connectors interconnect the two halves, the connectors being free of the shaft
According to a still further aspect of the invention, there is provided a traveling extrusion machine for forming hollow core concrete sections. The machine has a frame and a feed chamber mounted on the frame for receiving premixed concrete. A molding chamber is adjacent to the feed chamber. A non-rotatable mandrel shaft extends from the feed chamber to the molding chamber. A rotatable spiral conveyor is mounted on the mandrel shaft and extends from the feed chamber to the molding chamber. The conveyor has a first section within the feed chamber having flights with a fist constant external diameter. A second section of the conveyor adjacent to the molding chamber has flights with a second constant external diameter. The second diameter is greater than the first diameter. The second section extends along a portion of the conveyor. A third section of the conveyor is between the first section and the second section and has flights which taper from the first diameter to the second diameter. Preferably the second section has a plurality of flights.
The invention offers significant advantages over the prior art. One aspect of the invention provides a spiral conveyor for a concrete extrusion machine which is easily replaceable and is not subject to loss of components due to vibrations. Moreover, the replaceable section does not tend to become welded to the mandrel shaft or the remaining portion of the conveyor since bolts can be used to interconnect the two halves of the replaceable section, but the bolts do not engage the mandrel shaft or other portion of the conveyor. Instead a non-rotation locking device, such as a key and a keyway, are used to prevent rotation of the replaceable section relative to the main portion of the conveyor. The bolts may become frozen due to vibrations, but they can be removed simply by burning off the heads of the bolts or nut with a torch. No portion of the bolts or the replaceable section remains attached to the other portion of the conveyor.
Unlike the prior art, spiral conveyors and concrete extrusion machines according to another aspect of the invention provide a spiral conveyor section adjacent the molding chamber which has a fixed, increased diameter over a set distance along the conveyor. This arrangement appreciably decreases wear at that point compared with tapered conveyors which terminate abruptly adjacent the molding chamber. The larger end of the tapered section is where wear typically occurs. The invention extends the larger diameter of the conveyor a certain distance adjacent the molding chamber. In other words, the conveyor has a larger diameter straight section following the tapered section. The larger diameter straight section distributes the compression force over a greater area, accordingly decreasing wear and increasing the compression effect on the slab being formed.